In automated operations for the production of goods, such as during the manufacture and packaging of goods, the goods, packaging materials, etc. generally are conveyed along a processing or packaging path on an article conveyor. Such article conveyors typically include a conveyor belt or chain extended about a series of sprockets or rollers in a substantially endless loop. It is important that the conveyor chain or belt be under tension and have no slack therein as the chain is revolved around its conveying path. If slack is present in the conveyor chain, the chain potentially can slip or jump out of engagement with the teeth of the conveyor sprockets, especially where there is a limited engagement between the chain and the drive sprockets of the conveyor. Such jumping or slippage poses a significant danger to the operation of the packaging equipment, potentially disrupting the operation of the equipment or causing misfeeding of the articles, and thus damaging of the articles being conveyed. Overtensioning of the conveyor chain, however, leads to increased wear and reduced life of the conveyor chain, and requiring more often, costly replacement of the conveyor chain. Additionally, as space constraints in plants have increased, requiring reductions in the size of automated production and packaging equipment and article conveyors, the amount of engagement of the conveyor chains with the teeth of their drive and idler sprockets has decreased, increasing the chances of slippage or jumping of the conveyor chains.
To remedy the problems of loose or slack conveyor chains, chain tensioning or take-up devices have been developed for tensioning or taking up the slack of conveyor chains. Typically, such take-up mechanisms have included a ratchet and pawl mechanism that generally comprise a horizontally extending rack, one end of which is connected to a take-up sprocket for the conveyor chain, and a means for moving the rack and take-up sprocket longitudinally to tension and remove slack from the conveyor chain. The rack has a series of teeth formed along its upper edge and which are engaged by a spring loaded pawl as the rack is moved longitudinally. The pawl permits the rack to be moved in a first direction to move the take-up sprocket outwardly to take up any slack existing in the conveyor chain, while generally preventing significant rearward movement of the rack.
An example of such a conventional conveyor take-up or tensioning assembly is illustrated in U.S. Pat. No. 5,038,919 of Harston. The Harston patent generally discloses a conveyor system formed with two parallel, endless chains that carry transversely spaced flights. The conveyor assembly of Harston further includes spring loaded pawls that engage a ratchet bar, forming part of an adjustment means for adjusting the tension in the conveyor chain. An air cylinder is pressurized periodically to pull guide blocks, which support the conveyor chains and about which the conveyor chains are passed, outwardly to increase the tension in the conveyor chains. The engagement of the ratchet bar by the spring loaded pawls is designed to hold the tension in the conveyor chains.
The problem with such conventional take-up assemblies generally is that the tension in the conveyor chain can only be adjusted in discreet steps corresponding to the size of the teeth of the rack. Thus, if the rack is stopped with the pawl halfway between a pair of teeth of the rack, the rack will tend to slip back, commonly referred to as backlash, until the pawl engages a previous tooth recess of the rack. As a result, the conveyor chain at times will be slack when the pawl has slipped back to a previous tooth recess, and at other times will be under tension instead of a consistent tension being maintained on the conveyor chain during its operation.
Accordingly, it can be seen that a need exists for a conveyor tensioning assembly that enables the fine adjustment of tension in a conveyor chain without requiring such adjustment to be performed in finite, discreet steps and in which the potential for backlash of the conveyor chain is avoided to insure that a substantially constant tension is maintained in the conveyor chain.